Call RegisterStatsObserver after initializing video_stream_decoder_
Call RegisterStatsObserver after initializing video_stream_decoder_

Bug: webrtc:9091
Change-Id: I4e2f2d2f4677ed5916c6ae29e7fb56bf06c390f8
Tbr: 3824e10219998be3d28f43c1b42bf2b769d2c38c@webrtc.org
Reviewed-on: https://webrtc-review.googlesource.com/65640
Reviewed-by: Tommi <74a97831ec830b6e3846c6faa50560947ae01c68@webrtc.org>
Reviewed-by: Magnus Flodman <3824e10219998be3d28f43c1b42bf2b769d2c38c@webrtc.org>
Commit-Queue: Tommi <74a97831ec830b6e3846c6faa50560947ae01c68@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#22689}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc